Technical Field
The present invention relates to an optical image measuring apparatus for observing a measurement target using interference of light beams.
Background Art
In recent years, optical coherence tomography (OCT) has been drawing attention that acquires an image of the surface structure or the inner structure of a measurement target using interference of light beams. The OCT has already been put into practical use in funduscopy. In recent years, application of the OCT to imaging of cultured cells is also considered with a view to conduct inspection of transplanted tissue in regenerative medicine and the like.
In the OCT, as described in Patent Document 1, for example, a light beam from a light source is split into two: a signal beam to irradiate a measurement target and a reference beam to be reflected by a reference beam mirror without irradiating the measurement target. Then, the signal beam reflected by the measurement target is combined with and thus is caused to interfere with the reference beam, whereby an interference signal is obtained.
The OCT is broadly divided into the time domain OCT and the Fourier domain OCT depending on the method of moving the measurement position in the optical axis direction (hereinafter referred to as z-scan). In the time domain OCT, z-scan is performed by using a low coherence light source as a light source and moving a reference beam mirror during measurement. Accordingly, only the components in a signal beam that have the same optical path length as the reference beam interfere with the reference beam. When the obtained interference signal is subjected to envelope detection, a desired signal is obtained through demodulation. Meanwhile, the Fourier domain OCT is further divided into the wavelength-scanning OCT and the spectral domain OCT. In the wavelength-scanning OCT, z-scan is performed by using a wavelength-scanning light source capable of causing the wavelength of an emitted beam to scan, and causing the wavelength to scan during measurement. When Fourier transform is performed on the wavelength dependence of the detected interference beam intensity (i.e., interference spectrum), a desired signal is obtained. In the spectrum domain OCT, a broadband light source is used for a light source, and the following corresponds to the z-scan: splitting the generated interference beam using a beam splitter, and detecting the interference beam intensity (i.e., interference spectrum) for each wavelength component. When Fourier transform is performed on the obtained interference spectrum, a desired signal is obtained.